Generally speaking, food should be eaten fresh, as the fresher it is, the higher its nutritional value. But does this principle apply to all foods?
Fresh Vegetables
Many people enjoy vegetables and cook them immediately upon returning home while they are still fresh.Professor Lord Boschwell of the University of Maine's Food Science Department discovered that after one week of storage, tomatoes, potatoes, and cauliflower experience a decline in vitamin C content. Conversely, cabbage, melons, green peppers, and spinach show little change in vitamin C levels after a week. Refrigerated cabbage even contains more vitamin C than fresh cabbage.
Furthermore, extensive use of chemical fertilizers and other organic fertilizers—especially pesticides applied to control pests and diseases—is common. Sometimes, pesticides are even sprayed on vegetables just one or two days before harvest. It's best to store vegetables briefly before eating to allow residual harmful substances to gradually break down. For vegetables prone to spoilage, wash them thoroughly multiple times before consumption.
Fresh Wild Vegetables
Many city dwellers enjoy eating wild vegetables while visiting scenic areas. However, most wild vegetables now grow near garbage dumps or polluted waterways, making them difficult to clean thoroughly. Consuming contaminated wild vegetables can actually be harmful to health.
Fresh Milk
Reports indicate that farmers in certain cities have gained popularity by milking cows on the street and selling the milk fresh.However, Jia Jianbin points out that this practice is inadvisable. Freshly milked cows carry bacteria such as Brucella and tuberculosis bacilli, which can easily cause zoonotic diseases. Furthermore, the hygiene of the milking environment, the sterilization of containers, and the health status of the milkers cannot be guaranteed. Therefore, it is safer for consumers to purchase milk from reputable manufacturers at supermarkets.
Fresh Tea Leaves
"New tea" refers to leaves harvested within the past month, such as spring tea from the current season. Freshly processed spring tea contains potent tannic acids and alkaloids. Consuming large quantities can cause extreme nervous system stimulation, accelerating blood circulation and heart rate to produce intoxication-like symptoms including palpitations.Therefore, avoid brewing new tea too strongly or consuming it in excessive amounts. It is best to let it sit for a period, allowing the polyphenols to partially oxidize before drinking. Fresh Daylilies Avoid consuming fresh daylilies whenever possible. They contain colchicine, which can be absorbed through the intestines and converted into toxic substances within the body, causing poisoning.In contrast, dried daylilies undergo processes like steam fumigation and sun-drying during production, which remove most colchicine, making them safer. Since colchicine is water-soluble, fresh daylilies must be blanched or soaked before consumption. Dried daylilies should also be soaked briefly before use.
Fresh Wood Ear Mushrooms
Dried wood ear mushrooms are safer than fresh ones. Fresh wood ear mushrooms contain a specific compound called porphyrin. Porphyrin is a photosensitive substance. When consumed and exposed to sunlight, it can trigger phytophotodermatitis, causing skin itching, redness, swelling, and pain on exposed areas.Dried wood ear mushrooms are sun-dried products. Most porphyrin breaks down during sun exposure, and the remaining toxins dissolve in water during soaking, rendering the rehydrated mushrooms non-toxic. Note: Change the soaking water multiple times when rehydrating dried wood ear mushrooms.
Fresh Pickled Vegetables
Fresh vegetables naturally contain nitrates. During salt-pickling, these are reduced to nitrites. Nitrite levels peak before gradually being utilized or broken down by bacteria. Nitrites possess certain carcinogenic properties.Generally, the highest concentration of nitrites in pickled vegetables occurs within two to ten days after the pickling process begins. Therefore, it is best to wait at least twenty days after pickling before consuming them.
Jellyfish
Fresh jellyfish contain high water content, thick skin, and toxins. Only after undergoing three rounds of salting with alum (commonly known as "three alum treatments") to dehydrate the jellyfish three times can the toxins be fully expelled along with the water.After triple alum processing, jellyfish turns pale red or light yellow, with uniform thickness and resilience—squeezing it firmly yields no water. Only such jellyfish is safe to eat. When visiting jellyfish-producing regions, avoid purchasing or tasting unprocessed or only one- or twice-salted jellyfish.
Bottled Water
Most commercially bottled water—whether distilled, reverse-osmosis, mineral, or purified—undergoes final ozone disinfection before packaging. Consequently, freshly bottled water contains elevated ozone concentrations.Ozone is toxic to humans. Drinking it fresh means ingesting this toxin. If you let the water sit for 1-2 days, the ozone dissipates naturally, making it safe to drink without risk. By regulation, bottled water must pass inspection before leaving the factory—a process taking 48 hours. Thus, drinking water that has undergone proper factory testing is safe.